1. Technical Field
The present disclosure relates to a linear motion bearing assembly and, more specifically, to a hybrid linear motion bearing assembly having rolling elements positioned along a bearing track and a hydrostatic fluid supply passage adapted to receive a continuous source of hydrostatic fluid. The supply passage is in fluid communication with the bearing track to provide substantially friction-less movement between relatively movable parts.
2. Background of Related Art
Linear motion bearing assemblies having rolling elements, such as balls, pins or rollers, are well known and are utilized in various industries for movement of machine parts, tools and masses. Their use is especially conspicuous in the machine tool industry, where requirements of accuracy, stiffness, reliability and repeatability are stringent. Roller bearings are characterized as having relatively high load capacity, with good characteristics of function, static stiffness and accuracy. Typically, provisions are made for the circulation of the rolling elements via bearing retainers or end caps. The rolling elements are retained between two bodies along a bearing race. The bearing race has a tendency to act as a spring when a load is applied, wherein the amount of deflection of the bearing race is a function of the applied load. When a load having an oscillatory excitation is applied to the bearing, the bearing is subject to vibration which may adversely effect the bearing life, especially in terms of wear. Vibration may also adversely affect the precision of the apparatus to which the bearing is associated. For example, in a machining application, vibration may cause degradation of the surface finish of the article being machined.
Hydrostatic bearings, although not as prevalent as rolling element bearings, are also known. Hydrostatic bearings are characterized as having excellent low friction, accuracy, and repeatability characteristics, with a theoretically infinite life. Hydrostatic bearings also have excellent damping characteristics which result from hydrostatic fluid acting as a shock absorber between the apparatus to which the bearing is associated and an applied load. However, the overall load carrying capacity of hydrostatic bearings, as well as static stiffness, are not as high as those of rolling element bearings.
Accordingly, a need exists for an improved bearing having excellent damping characteristics, a relatively high load capacity, and excellent characteristics of friction, static stiffness, accuracy and repeatability.